Asynchronous transfer mode (ATM) is a widely-used communications packet-switching technology. All-optical ATM networks will almost inevitably have to buffer (temporarily store) optical ATM cells (packets) when routing the cells to their appropriate destinations. This storage requirement can be met by an all-optical-loop buffer, provided that the buffer can store the optical ATM cells for multiple circulations around the loop.
Implementations of all-optical-loop buffers for ATM cells have been demonstrated in the past. Most loop buffer implementations consist of semiconductor optical amplifiers (SOAs) and erbium-doped fiber amplifiers (EDFAs) that work in tandem to store an optical ATM cell for several circulations. These buffers have been able to store an ATM cell only for too-few circulations around the buffer and hence for too-short a period of time, due to the reduction of the extinction ratio of the circulating ATM cell as it loops around in the buffer. The extinction ratio is the ratio of the optical-energy level of a binary "1" to that of a binary "0" level of a modulated signal. A desirable extinction ratio is generally about 30dB or better. The reduction in the extinction ratio is caused by the increased saturation of the SOAs by the EDFAs as the cell repeatedly traverses the optical-loop buffer. Ideally, the cell's extinction ratio should not be degraded as a consequence of using the optical-loop buffer.